1. Field of the Invention
The present invention relates generally to electrostatically actuated cantilever switches and more particularly relates to microwave stripline switches capable of actuation with reduced voltage requirements and lower switch impedance.
2. Description of the Related Art
Changes in integrated circuits have been possible due to recent developments in microfabrication techniques. These changes have been addressed to making the devices smaller, more efficient, and capable of large scale production at low cost. More specifically, micromachining includes the techniques of planar technology, wet chemical etching and other etching techniques, metalization, and metal deposition.
The present inventive concept includes a basic electrostatically actuated cantilever switch. The uses for this type of switch vary from reactive (especially inductive and/or tuned) elements, microrelays, microsensors, to microsized switches in microwave stripline circuits.
It is well known in the prior art to fabricate in a batch process microelectronic switches.
Prior art methods of configuring electrostatically actuated switches have included microstrip lines divided into a number of short sections, each capacitively coupled to its neighbor by a cantilever switch. The cantilever makes contact with an element which serves as both the pull down electrode and the contact pad.
Other prior art uses the electrostatically actuated cantilever switch with the pull down electrode and the contact pad split into two separate elements. However, these elements have been arranged in a manner that placed the pull down electrode under the middle portion of the cantilever beam. The contact pad was placed under the unattached end of the cantilever beam. In other words, the contact pad was placed further from the cantilever fulcrum then what the pull down electrode was placed.
The U.S. Pat. No. 3,539,705 issued to H. C. Nathanson et al., on Nov. 10, 1970, entitled, "Microelectronic Conductor Configurations and Method of Making the Same" describes small air gap metal structures batch fabricated as part of a microelectronic component. These spaced metal elements can be optionally closed by compression bonding.
U.S Pat. No. 3,796,976 to Heng, et al., issued Mar. 12, 1974, entitled "Microwave Stripline Circuits with Selectively Bondable Micro-Sized Switches for In Situ Tuning and Impedance Matching", describes a microstrip line divided into a multiplicity of short sections, each capacitively coupled to its neighbor by a cantilever switch. These novel switches were of a predetermined length, (equal to fractions of a desired wavelength) and are connected together to shift the phase of energy propagating along their length thereby tuning and impedance matching the microstrip circuits.
U.S Pat. No. 4,674,180 to Zavracky et al., issued Jun. 23, 1987, entitled "Method of Making a Micromechanical Electric Shunt", describes a miniature electrical shunt exhibiting hysteresis taking the form of a modified cantilever beam element fabricated by microfabrication and micromachining techniques.
As can be seen in the above referenced patents, it is well known in the prior art to fabricate compression bonded microelectronic switches. However, the configuration of these switches results in higher voltages than necessary for actuation.
An object of the present invention is to provide an electrostatically actuated cantilever switch with a reduce pull down voltage.
Another object of the present invention is to provide an electrostatically actuated cantilever switch with a low impedance.
These and other objects are accomplished by an electrostatically actuated cantilever switch, which comprises: an insulating substrate with a pull down electrode and a contact pad attached to the substrate top surface. A cantilever beam element which has a first end portion attached to the substrate top surface. The cantilever element has an opposite end portion extending over but not touching the pull down electrode. Additionally, the cantilever element has a center portion extending between the first and second end portions positioned over but not touching the contact pad. A means for establishing an electrostatic charge attraction between the cantilever beam and the pull down electrode is used. This results in the end portion of the cantilever element deflecting towards the pull down electrode. The deflection in the cantilever element causes the cantilever element and the contact pad to make contact.
In another aspect of the present invention, the electrostatically actuated switch serves as a better baseline element for use in phase shift methods.
These and other features and advantages of the present invention will become more apparent with reference to the following detailed description and drawings.